1. Field of the Invention
The present invention relates to an improved registration control in an intermittent motion type decorating machine for increasing the quality of printed indicia and precision of indicia registration on a workpiece and, more particularly, to improving the interrelationship and construction of drive components used for synchronously moving a decorating screen and a workpiece to apply decoration to workpieces especially to avoid registration errors in the placement of multicolor decorations in a given decoration area of a workpiece.
2. Description of the Prior Art
As shown in U.S. Pat. Nos. 2,231,535; 2,261,255; 2,721,516; 3,251,298; and 5,524,535 intermittent motion type decorating machines are known in the art and provide an indexing drive system to impart intermittent traveling motion to an endless chain conveyor used to supply workpieces such as containers made of glass or plastic. A container is moved by the endless chain conveyor through a predetermined distance, stopped, moved again through a predetermined distance, stopped and again moved until each container through the sequence of motions moves completely through each of all of the decorating stations of the decorating machine. A decorating station is provided at one or more places along the conveyor. A decorating screen is displaced by an associated squeegee into line contact with the surface of the container while the container is stopped from traveling motion and the container is rotated about a longitudinal axis thereof During the decorating process a synchronous speed relation must be maintained between the linear displacement of the screen and the peripheral speed of the rotating container at the line of contact established by the squeegee. The squeegee remains stationary during the decorating process. Decorating machines of this type are particularly useful to decorate bottles and carryout the decoration while the surface of the bottle being decorated is horizontally oriented.
In the above U.S. Pat. No. 2,261,255 there is disclosed a drive for moving each of a body screen to decorate a cylindrical body of a bottle and a shoulder screen to decorate a tapered or straight neck portion of the bottle at the corresponding peripheral and linear speeds. The decorating machine disclosed in the aforesaid U.S. Pat. No. 3,251,298, provided a production rate of about 125 bottles per minute. The decoration is carried out by dividing a machine cycle into two decoration cycles, each essentially made up of two equal parts. One half each decoration cycle is used for the decoration of a workpiece and the remaining half the decoration cycle is used for indexing movement of the bottles by the conveyor through the decorating machine. There is no overlap between the decorating and indexing cycles. During the first part of the decoration cycle, the decoration screen is moved along a linear path in only one direction at a speed that is synchronous with the peripheral speed of the decoration receiving surface of the rotating bottle to avoid smearing the printing media. The drive for the entire decorator is powered by a single motor to synchronize the operation by various drive trains to maintain a timed sequence at synchronous speed of operation by a screen drive and a bottle rotator. When the decoration screen moves to the end of its linear path of travel, the bottle rotator completes a rotation cycle of 360.degree.. The second part of the decoration cycle, powered by the drive motor, provides that the screen drive enters a dwell period to maintain the decoration screen stationary for the remaining part of the decoration cycle while the decorated bottle is removed from the decorating station and an undecorated bottle is installed at the decorating station. The newly installed bottle at the decorating station is decorated by the same timed sequence of operation in the second decorating cycle of the machine cycle. Important, however, is the fact that the operation of the same decorating screen in the second decorating cycle is accomplished by reversing the linear travel of the decorating screen by providing a continuous cam track of a rotating cam used to drive the decorating screen in a reverse direction of screen travel for decoration of a workpiece in the second decorating cycle of the machine cycle. This reversal to the direction of screen travel necessarily requires the drive elements transmitting torque between the screen drive cam and the decorating screen to pass from one state of torque transmitting, and metal-to-metal relationship through necessary operating clearances in the drive train and into a different state of torque transmitting, metal-to-metal relationship during displacement of the decorating screen in the reverse direction of travel. The machine cycle uses a preestablished position relationship between the decoration site on the bottle surface and the pattern of decoration in the decorating screen. This preestablished position relationship is created by providing a registration station at the entry end of the workpiece conveyor for rotating each bottle about the longitudinal axis of the bottle into a preestablished orientation in a bottle carrier that is part of the workpiece conveyor of the decorating machine.
In U.S. Pat. No. 3,338,574, there is shown a workpiece carrier device for supporting a bottle in a horizontal orientation while intermittently moved along a path of travel through a decorating apparatus. The bottle is supported at its opposite ends by clamping chucks one of which has a journal extending from a bearing support and the other of which can move releasably to contact a bottle for causing rotation about a horizontal axis. The bottle is rotated by a drive member brought into a driving relation with the protruding journal part of the bearing support. The clamping chucks are operatively supported on a base secured to chain-links forming an endless conveyor chain extending along the path of travel of bottles through the decorating apparatus.
Robustly constructed drives are necessary to withstand the forces of inertia and impact loading which occur due to the intermittent conveyor motion moving the bottles to and from each of the decorating stations, the rotation of each bottle for the decorating process and the drive mechanism for reciprocating each decorating screen at each decorating station. More recently as disclosed in U.S. Pat. No. 5,524,535 an improved intermittent decorating machine cycle is provided to increase the rate for decorating bottles. Two decorating cycles making up a machine cycle are each provide that during the decoration cycle a portion for conveyor indexing has a reduced duration to provide an increase to the duration of the decoration cycle in which the screen is linear displaced while the bottle is rotated for decoration.
In such intermittent motion decorating machines, thermosetting ink is usually the printing medium particularly when multiple color decoration is needed. Ink of only one color is applied at each decorating station and to decorate with multiple colors requires corresponding multiple decoration stations. When the different colors interleave in a given area of the bottle, the same area is contacted with the screens for each color and therefore it is necessary that the applied ink/color is solidified and will not smear when additional ink/color is applied. Although the ink is solidified after each printing operation, curing the ink by feeding the bottles through a furnace after discharging from the decorating machine is necessary. In co-pending patent application Ser. No. 09/079,753 filed May 15, 1998 there is disclosed an intermittent decorating machine providing curing of ink decoration applied at one station before additional decoration is applied so that the decoration on a bottle delivered from the decoration machine is cured and the bottle can be loaded directly into a shipping container without the need for curing the ink decoration. The decorating medium cures very rapidly when exposed to electromagnetic wave energy such as ultraviolet radiation or heat. Curing stations are interleaved between printing stations and a drive to rotate a bottle at a printing station is linked with a drive to rotate a bottle at a curing station for exposing uncured printing medium to the electromagnetic wave or heat to curing the printing medium. The dwell period of the intermittent advancing motion by the conveyor chain is used to apply decoration and to cure the applied decoration all at difference spaced apart sites along travel by the bottles in the decorating machine.
At each decorating station there is a rotator drive head provided with a slot opening to receive a roller on the end of a crank arm by which a bottle is rotated for the decorating process. The rotational axis of the bottle and the rotational axis of the drive head must be aligned to produce a uniform rotational speed of the bottle surface to which decoration is applied. As each bottle carrier is advanced by the chain conveyor to a decoration station, rollers that are part of each of the parallel runs of chain are displaced vertically from the horizontal path of travel by carrier riser cams. The bottle on the carrier is lifted, a relatively small but sufficient distance, to avoid impact by the decorating screen during its necessary reciprocating movement with bottles on adjacently located carriers. Wear of the chain rollers and the riser cams cause a change to the preset elevation of the carrier at the decorating station which in turn fails to bring the rotation axis of the bottle into coaxial alignment with the rotation axis of the bottle rotator. This lack of coaxial alignment produces nonconcentric rotation between the rotational axis of the bottle and the rotator. As a result, the applied decoration is distorted because of slippage due to the mismatch of speeds between the decorating screens and the rotation of the bottle surface.
Other factors have an adverse influence to the elevation at which bottles are delivered by the conveyor for a dwell period for decoration at a printing station. One such factor is dimensional variations occurring during the manufacture of "L" shaped lugs of which three and sometimes four such lugs are used to mount bottle carriers to conveyor chains of the conveyor. The dimensional variations occur randomly as errors to the drilled location of apertures in "L" shaped lugs and variations to the precision of bending bar stock to the required "L" shaped configuration. Another factor is backlash between meshing gear teeth of a drive gear mounted on the bottle rotator and a gear rack reciprocated in response to reciprocation of the decorating screen. The backlash can be eliminated through periodic adjustments to the elevation of the gear rack but are made periodically to correct for an unacceptable mismatch of speeds between the reciprocation of the decorating screen and rotation of the bottle surface. This backlash also adversely affects the start and stop location of the bottle rotator.
One aspect of the present invention is particularly useful for controlling intermittent motion decorating machines constructed to apply decoration in each of opposite directions of reciprocation by a decorating screen. There are significant disadvantages to the existence of a continuous mechanical interlocking relation formed by the meshing relationship between the drive gear mounted on the bottle rotator and the meshing gear rack driven through a mechanically connected drive to reciprocate with reciprocation of the decorating screen. The mechanical interlocking relation adversely effects the precision with which decoration is applied to designated decoration areas of successive bottles. A first relationship is established between the screen and a decoration area of the receiving bottle after all operating clearances of the bottle rotator and screen reciprocating drive are eliminated by a metal-to-metal relation for transmitting torque. A second relation is established which differs from the first relation as a result of the aggregate of the operating clearances traversed by the machine parts in the drive system when reversed to displace the screen in a return direction linearly. When the direction of screen displacement is reversed from the return direction there is a return to the first relationship because the screen drive is mechanically coupled continuously to the gear rack system of the bottle rotator. A feature of the present invention provides for the decoration of successive bottles by a decorating screen only when the screen is linearly displaced in the same direction and when the travel of the screen is reversed the bottle rotator is uncoupled from the driving relationship with the screen drive to prevent impact between the crank arm of a bottle carrier entering the decorating station with the rotator. By avoiding the reversing revolution of the rotator, the drive slot is at an orientation or can be correctively positioned to a required orientation for receiving a crank arm of a bottle support for the next bottle entering the decorating station.
It is an object of the present invention to provide an improved construction and operation for an intermittent motion decorator having a workpiece rotator coupled by a drive controller to a screen drive used to linearly displace a decorating screen synchronously with rotation of a workpiece and after the application of decoration, the drive controller is operable to uncouple the rotator from the screen drive.
It is a further object of the present invention to provide an intermittent motion decorator having at least two decorating stations separated by a distance along which guides maintain orientation of workpiece crank arms used to prevent the loss of workpiece orientation during the indexing and rotate a workpiece at each decorating station after mechanically coupled to a rotator driven by an electric motor controlled by an electronic linear motion detector responsive to displacement of a decorating screen when applying decoration to the workpiece.
It is another object of the present invention to provide an intermittent motion decorator embodying a drive operatively controlled to rotate a workpiece for the application of decoration only during displacement of a decorating screen in one direction and not in the second reversing direction during which a successive workpiece is advanced by intermittent motion to the decorating station and the workpiece rotator is non responsive to the return of the decorating screen.
It is another object of the present invention to provide an intermittent motion decorator having the workpiece rotator driven by an electric motor controlled for intermittent operation only during the application of decoration, the workpiece rotator being vertically movable for accommodating changes to the elevation at which the rotational axis of a workpiece rotator resides at a decorating station during operation of the workpiece rotator.
It is yet a further object of the present invention to provide an electric control system for correcting position error of a workpiece rotator after decorating a first workpiece to insure a driving relation established with a second workpiece in an intermittent motion decorator to faithfully maintain both workpiece orientation and synchronous speed relation between linear displacement of a decorating screen and surface speed of a rotating workpiece, particularly in intermittent motion decorator machines having a decorator drive cam constructed for unidirectional decorating.